Two general processes can be applied for synthesis of organosiloxane polymers; ring opening polymerization of cyclic siloxanes and polycondensation. The polycondensation reaction between organofunctional silanes or oligosiloxanes leads to the formation of siloxane bond and elimination of a low molecular byproduct. The polycondensation of low molecular weight siloxanol oils is the most common method synthesis of polyorganosiloxanes and has been practiced for several years. The byproduct of this process is water. Unfortunately this method cannot be used for the synthesis of well-defined block organosiloxane copolymers. In that case the non-hydrolytic condensation processes can be employed. Many of such reactions are known and are frequently used:    1) the reaction of an organohalosilane with an organoalkoxysilane, ≡Si—X+R—O—Si≡→≡Si—O—Si≡+RX;    2) the reaction of organohalosilanes with organoacyloxysilanes, ≡Si—X+RCOO—Si≡→≡Si—O—Si≡+RCOX;    3) the reaction of organohalosilanes with organosilanols, ≡Si—X+HO—Si≡→≡Si—O—Si≡+HX;    4) the reaction of organohalosilanes with metal silanolates, ≡Si—X+Metal—O—Si≡→≡Si—O—Si≡+MetalX;    5) the reaction of organo-hydrosilanes with organosilanols, ≡Si—H+HO—Si≡→≡Si—O—Si≡+H2;    6) the self-reaction of organoalkoxysilanes, ≡Si—OR+RO—Si≡→≡Si—O—Si≡+ROR    7) the reaction of organoalkoxysilanes with organoacyloxysilanes, ≡Si—OR+R′COO—Si≡→≡Si—O—Si≡+R′COOR    8) the reaction of organoalkoxysilanes with organosilanols, ≡Si—OR+HO—Si≡→≡Si—O—Si≡+ROH    9) the reaction of organoaminosilanes with organosilanols, ≡Si—NR2+HO—Si≡→≡Si—O—Si≡+NR2H;    10) the reaction of organoacyloxysilanes with metal silanolates, ≡Si—OOR+Metal—O—Si≡→≡Si—O—Si≡+MetalOOR;    11) the reaction of organoacyloxysilanes with organosilanols, ≡Si—OOR+HO—Si≡→≡Si—O—Si≡+HOOR;    12) the reaction of organooximesilane with organosilanols, ≡Si—ON=OR2+HO—Si≡→≡Si—O—Si≡+HN=OR2;    13) the reaction of organoenoxysilane with organosilanols, ≡Si—O(C=CH2)R+HO—Si≡→≡Si—O—Si≡+CH3COR;
Those reactions can also be used for the formation of siloxane networks via a crosslinking process. Many of the above processes require the presence of catalyst such as protic acids, Lewis acids, organic and inorganic bases, metal salts and organometalic complexes. (See, for example, (a) “The Siloxane Bond” Ed. Voronkov, M. G. ; Mileshkevich, V. P. ; Yuzhelevskii, Yu. A. Consultant Bureau, New York and London, 1978; and (b) Noll, W. “Chemistry and Technology of Silicones”, Academia Press, New York, 1968).
It is also well known in silicon chemistry that the organosilanol moiety will react with a hydrogen atom bonded directly to silicon (organo-hydrosilane) to produce a hydrogen molecule and the silicon-oxygen bond, (See, “Silicon in Organic, Organometallic and Polymer Chemistry” Michael A. Brook, John Wiley & Sons, Inc. , New York, Chichester, Weinheim, Brisbane, Singapore, Toronto, 2000). Although the uncatalyzed reaction will run at elevated temperatures, it is widely known that this reaction will run more readily in the presence of a transition metal catalyst especially noble metal catalysts such as those comprising platinum, palladium, etc. , a basic catalyst such as an alkali metal hydroxide, amine, etc. , or a Lewis acid catalyst such as a tin compound, etc. Recently it has been reported that organo-boron compounds are extremely efficient catalysts for the reaction between an organo-hydrosilanes and organosilanols (WO 01/74938 A1). Unfortunately, the by-product of this process is dangerous, highly reactive hydrogen.
Another useful class of materials, polyaryloxysilanes (PAS) have long been materials of commercial interest. In addition to the property benefits expected for any silicone copolymer, such as good low temperature flexibility, high temperature stability PAS also exhibit excellent flammability characteristics.
These polymers are commonly prepared by the reaction of bis-phenols with α, ω-difunctional silanes, typically, α, ω-dichlorosilanes or α, ω-diaminosilanes. Reaction of bis-phenols with α, ω-dichlorosilanes requires the use of a stoichiometric amount of an acid acceptor, usually a tertiary amine. As the ether linkage in these polymers is susceptible to hydrolysis, particularly in the presence of acid or base, the amine and its salts must be completely removed from the polymer for optimal stability. The α, ω-diaminosilanes do not require an acid scavenger during the preparation of the polymer, but these intermediates themselves are prepared by the reaction of chlorosilanes with amines in the presence of an acid acceptor.
In spite of the foregoing developments, there is a continuing search for new condensation reactions that will improve reaction's selectivity and safety of the polycondensation process.